Composition and method for treating tin plated steel surface

ABSTRACT

A superior protective prepainting treatment for tin plated steel surfaces, particularly DI cans, may be achieved by contacting the surface with an aqueous liquid composition containing from 1 to 30 g/L of phosphate ions, from 0.1 to 5 g/L of condensed phosphate ions, from 0.5 to 5 g/L of reducing agent, and from 0.1 to 20 g/L of dissolved solids of a water soluble aminated poly{vinyl phenol} resin.

TECHNICAL FIELD

The present invention relates to a liquid composition and process fortreating a surface of tin-plated steel, particularly the surface ofdrawn and ironed (hereinafter "DI") tin cans. The process imparts anexcellent corrosion resistance and paint adherence to the surface ofsuch a can after its formation by the draw-ironing of tin-plated steelsheet but before its painting or printing. The process and compositionalso impart the excellent slideability which is required for the smoothconveyor transport of such a can (designated briefly below as simply"slideability")

BACKGROUND ART

In the field of liquid compositions for treating the surface oftin-plated DI can, one example of related art is the invention disclosedin (1) Japanese Patent Application Laid Open [Kokai or Unexamined]Number 01-100,281 [100,281/89] by the assignee of the presentapplicants. This particular invention comprises a film-forming liquidcomposition for the treatment of metal surfaces in which the liquidcomposition has a pH of 2 to 6 and contains 1 to 50 g/L phosphate ion,0.2 to 20.0 g/L oxyacid ion, 0.01 to 5.0 g/L tin ion, and 0.01 to 5.0g/L condensed phosphate ion. Treatment with this liquid composition laysdown a strongly corrosion-resistant phosphate film on the surface oftin-plated DI can.

In addition, the invention disclosed in (2) Japanese Patent ApplicationLaid Open Number 01-172,406 [172,406/89] is an example of a treatmentmethod intended to develop corrosion resistance and adherence throughthe use of water soluble resin. This invention comprises a method fortreating metal surfaces with a solution which contains a derivative of asuitable polyhydric phenol compound.

Furthermore, during the metal can manufacturing process, the highfriction coefficient of the exterior can surface causes the can surfaceto have a poor slideability during conveyor transport of the can, whichoften causes the can to tumble over sideways and thus impairs thetransport operation. Can transportability is a particular issue withrespect to transport to a printer. It is therefore necessary in thecan-manufacturing industry to reduce the static friction coefficient ofthe exterior can surface without compromising the adherence of any paintor lacquer to be coated on the can. The invention disclosed in (3)Japanese Patent Application Laid Open Number 64-85292 [85,292/89] is anexample of a method for improving the slideability. This inventionconcerns an agent for treating the surfaces of metal cans. Thisparticular agent contains water soluble organic material selected fromphosphate esters, alcohols, monovalent and polyvalent fatty acids, fattyacid derivatives, and mixtures of the preceding.

It has already been discovered that a film with an excellent corrosionresistance, excellent paint adherence, and improved slideability can beformed on the can surface through the use of a surface treatment liquidcomposition which characteristically comprises an aqueous solution witha pH of 2.0 to 6.5 which contains 1 to 30 g/L of phosphate ions, 0.1 to5 g/L of condensed phosphate ions, and 0.1 to 20 g/L (as solids) of awater soluble resin (poly{vinyl-phenol-amino} compound). This has beenthe subject of an antecedent patent application (Japanese PatentApplication Number 02-160,443 [160,443/90]).

DESCRIPTION OF THE INVENTION Problem to Be Solved by the Invention

The invention in the above described related art example (1) consists ofa method for the formation of a phosphate film on the surface of DI tincans. The tin-plated DI can produced over the last few years has carriedsmaller quantities of tin plating in response to economic pressures, andthis has necessitated surface treatments with a far better corrosionresistance than before. However, the required substantial improvement incorrosion resistance lies beyond the capacity of the phosphate filmformed in the above-described art example (1).

The invention in the above described art example (2) involves the use ofa polyhydric phenol compound. However, a satisfactorily stableperformance (corrosion resistance) is not always obtained by treatingtin-plated DI can by this method.

The invention in the above described art example (3) does in factimprove the slideability to some degree, but it does not improve thecorrosion resistance or paint adherence of tin-plated DI cans.

Finally, in the case of the invention of the antecedent application, theresin is precipitated by the eluting tin ion when tin-plated DI can iscontinuously treated, and this impairs the industrial utility of thismethod.

Thus, with respect to the treatment of tin-plated DI cans, there isdemand in the art for a treatment liquid composition (a) which generatesa film which simultaneously provides an excellent corrosion resistance,paint adherence, and slideability and (b) which itself presentsexcellent process characteristics, capable of supporting continuoustreatment. However, relative to this property spectrum both theabove-described related art examples and the invention of the antecedentapplication suffer from problems which would be advantageous to solve.

SUMMARY OF THE INVENTION

As a concrete means for solving the aforementioned problems which arisein the above-described art examples and with the invention of theantecedent application, the present invention proposes a liquidcomposition for treating the surface of tin-plated DI can, where saidliquid composition characteristically has a pH of 2.0 to 6.5 andcomprises, preferably consists essentially of, or more preferablyconsists of, water and 1 to 30 grams per liter (hereinafter "g/L") ofphosphate ions, 0.1 to 5 g/L of condensed phosphate ions, 0.5 to 5 g/Lof reducing agent, and 0.1 to 20 g/L (as solids) of water-soluble resinwith the following general formula: ##STR1## where, in the precedingformula, n is an integer with a value in the range from 2 to 80 forindividual molecules in the resin but may have a non-integral averagevalue for the resin component as a whole; each of X and Y independentlyof each other and independently for each unit in the molecule mayrepresent hydrogen or a group "Z" with the following formula: ##STR2##in which each of R₁ and R₂ independently of each other and independentlyfor each Z group in the component represents a C₁ to C₁₀ alkyl and/orhydroxyalkyl moiety; and the total number of Z groups present in theresin component is from 30 to 200% of the total number of aromatic ringsin the resin component.

This liquid composition for treating the surface of tin-plated DI canhas excellent process characteristics which make possible continuoustreatment and also generates a film which simultaneously provides anexcellent corrosion resistance, paint adherence, and slideability.

DETAILS OF PREFERRED EMBODIMENTS OF THE INVENTION

The surface-treatment liquid composition according to the presentinvention comprises an acidic treatment liquid composition whoseessential components are phosphate ion, condensed phosphate ion,reducing agent, and water soluble resin.

The phosphate ions can be introduced into the treatment liquidcomposition using phosphoric acid (H₃ PO₄), sodium phosphate (Na₃ PO₄),and the like. Their content should fall within the range preferably of 1to 30 g/L and more preferably of 5 to 15 g/L. At phosphate ionconcentrations below 1 g/L, the reactivity is poor and film formationwill not usually be satisfactory. While a good-quality film can beformed at values in excess of 30 g/L, the cost of the liquid compositionis increased and the economic value is impaired.

The condensed phosphate ions comprise at least one selection frompyrophosphate ions, tripolyphosphate ions, and tetrapolyphosphate ions.An acid and/or salt can be used to introduce the condensed phosphateion. For example, when the pyrophosphate ion is to be introduced,pyrophosphoric acid (H₄ P₂ O₇), sodium pyrophosphate (Na₄ P₂ O₇), andthe like can be used. This component should preferably be present at 0.1to 5 g/L, and the range of 0.4 to 1 g/L is particularly preferred. Atvalues less than 0.1 g/L, a satisfactory film will not normally beformed, due to the weak etching activity. However, the etching activityis too high at values in excess of 5 g/L, and the film forming reactionis usually inhibited.

The reducing agent is not specifically restricted, but it preferablyconsists of phosphorous acid and/or hypophosphorous acid and/or theirsalts. While its content will be governed by the reducing power of theparticular reducing agent, the general range of 0.5 to 5 g/L ispreferred. At concentrations less than 0.5 g/L, a satisfactory effect isoften not developed by this component due to the weak reducing activity.The cost of the treatment liquid composition is increased and theeconomics become problematic at reducing agent concentrations in excessof 5 g/L. As an example, the acid or salt can be used to introducephosphorous acid or hypophosphorous acid, and their preferred additionis 1 to 3 g/L, measured as the stoichiometric equivalent as acid.

The water soluble resin used by the present invention has the followinggeneral formula: ##STR3## in which n has a value of 2 to 80. Themolecular weight is too low at values of n below 2 and no improvement incorrosion resistance for the treated tin plate will normally beobserved. At values of n=81 and above, the aqueous solution has areduced stability which will normally generate problems in practicaluse.

The groups R₁ and R₂ in the general formula for the groups Z alreadygiven above are C₁ to C₁₀ alkyl and/or hydroxyalkyl groups. Functionalgroups containing 11 or more carbons reduce the stability of the aqueoussolution. The group Z is preferably --CH₂ N(CH₃)CH₂ CH₂ OH or --CH₂N(CH₃)₂.

The number of groups Z should be 30 to 200% of the number of aromaticrings in the above-described resin polymer. Thus, when five Z groups arepresent in a polymer with n=10, the ratio of Z's to aromatic rings isthen 50%. Ratios below 30% cause the resin to be poorly water solubleand thus risk stability problems. (Ratios higher than 200% would beinconsistent with the general formula for the resin.)

The specified water soluble resin should be present at 0.1 to 20 g/L ona solids basis. Resin concentrations less than 0.1 g/L make stable filmformation on the can surface highly problematic. Concentrations inexcess of 20 g/L are uneconomical due to the increased cost of thetreatment solution.

The pH of the treatment liquid composition must be in the range from 2.0to 6.5. Etching is heavy and film formation is impaired at pH valuesless than 2.0. At pH values in excess of 6.5, the liquid compositionlife is shortened because the resin tends to precipitate and sediment.The pH can be adjusted as needed through the use of an acid, forexample, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoricacid, or the like, or through the use of a base, for example, sodiumhydroxide, sodium carbonate, ammonium hydroxide, or the like.

The method for preparing the surface-treatment liquid compositionaccording to the present invention can be briefly explained as follows.Prescribed quantities of phosphate ions, condensed phosphate ions, andreducing agent as described above are dissolved in water with thoroughstirring. When the pH of this liquid composition is not already lessthan 7, it is adjusted to below 7 using the appropriate acid as listedabove. The water soluble resin specified by the present invention isthen added and completely dissolved while stirring, and the pH isadjusted as discussed above if not already within the desired range.

The film which is formed by contact of the surface treatment liquidcomposition of the present invention with tin plate is anorganic/inorganic composite film which is composed of the resin andphosphate salts, with the main component of the phosphate salts beingtin phosphate. The substrate is etched by the phosphate ion andcondensed phosphate ion, the pH at this time is locally increased at theinterface, and phosphate salt is deposited on the surface. Moreover, theamino groups in the resin have a chelating activity, and probably form acoordination compound with the fresh surface of the substrate generatedby etching. The organic/inorganic composite film is formed byessentially these two mechanisms. The simultaneous presence of thecondensed phosphate ion probably promotes formation of the resin/metalcoordination compound, and this would facilitate the stable formation ofthe organic/inorganic composite film on the surface over a broad pHrange.

The process for treating tin-plated DI can using the surface-treatmentliquid composition of the present invention will now be considered. Thetreatment liquid composition can be applied by any method that achievesadequate contact between the liquid composition and the metal surface tobe treated for an adequate time. The following process steps constitutea preferred example of a suitable process according to this invention.

1. Surface cleaning of the tin-plated DI can: degreasing (a weaklyalkaline cleaner is typically used)

2. Tap water rinse

3. Film-formation treatment (application of the treatment liquidcomposition according to the present invention)

treatment temperature: ambient to 80° C.

treatment method: spray

treatment time: 2 to 60 seconds

4. Tap water rinse

5. Rinse with de-ionized water

6. Drying

A surface treatment liquid composition according to the presentinvention can be used at treatment temperatures from room temperature(i.e., about 20° C.) up to 80° C.; however, it is preferably usedgenerally heated to 40° to 60° C. The contact time should be 2 to 60seconds. At less than 2 seconds, the reaction is generally inadequateand a highly corrosion resistant film will not be formed. No improvementin performance is observed for treatment times in excess of 60 seconds.Accordingly, the most useful treatment times will fall in the range of 2to 60 seconds. Contact is preferably by spraying, at least on objectssuch as tin cans with only one surface plated, in order to avoid wasteof treatment materials by unnecessarily treating the unplated side, aswould result from immersion contact.

The superior utility of the surface-treatment liquid compositionaccording to the present invention will be illustrated in the followingthrough the use of examples and comparison examples.

EXAMPLES AND COMPARISON EXAMPLES General Test Methods and Procedures

The corrosion resistance of treated cans was evaluated using the ironexposure value ("IEV"), and the IEV was measured in accordance with theinvention of U.S. Pat. No. 4,332,646. The corrosion resistance is betterat lower IEV values, and a score below 150 is generally regarded asexcellent.

The paint adherence was evaluated based on the peel strength as follows:The surface of the treated can was coated with an epoxy/urea can paintto a film thickness of 5 to 7 micrometers; this was baked at 215° C. for4 minutes; the can was then cut into a 5×150 mm strip; a test specimenwas prepared by hot-press adhesion with polyamide film; and this waspeeled by the 180° peel test method. Accordingly, the paint adherenceincreases as the peel strength increases, and values in excess of 1.5kgf/5 mm-width are generally regarded as excellent.

The slideability was evaluated by measuring the static frictioncoefficient of the exterior surface of the can. Thus, the slideabilityimproves as the static friction coefficient declines, and values below1.0 are generally regarded as excellent.

Finally, the stability of the compositions was evaluated as follows.First, tin-plated DI can (manufactured by the DI-processing oftin-plated steel sheet) was degreased using a 1% hot aqueous solution ofa weakly alkaline degreaser (FINECLEANER™ 4361A, commercially suppliedby Nihon Parkerizing Company, Ltd.). One immersion cycle consisted ofimmersing the degreased can for 2 minutes in 1 L of the particularsurface treatment liquid composition heated to 60° C. After 10 cycles,the surface treatment liquid composition was inspected for resinprecipitation. The stability was considered to be excellent when resinprecipitation was absent.

Example 1

Tin plated DI can was prepared by draw-ironing tin plated steel sheet.It was cleaned with a 1% hot aqueous solution of a weakly alkalinedegreaser (FINECLEANER™ 4361A, registered brand name of NihonParkerizing Company, Ltd.), then sprayed with surface-treatment liquidcomposition 1, heated to 60° C., for 30 seconds, then washed with tapwater, sprayed with de-ionized water (with a specific electricalresistance of at least 3,000,000 ohm-cm) for 10 seconds, and, finally,dried in a hot air-drying oven at 180° C. for 3 minutes. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 1 was also evaluated.

Surface-Treatment Liquid Composition 1

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

phosphorous acid (H₃ PO₃)

2.0 g/L (providing 1.9 g/L of PO₃ ³⁻ ions)

resin solids

2.0 g/L of water soluble resin 1 (see below)

pH=4.0 (adjusted with sodium hydroxide)

water soluble resin 1 had, in the general formula given above, anaverage value for n of 40, half the total of X's and Y's in the generalformula as Z, and Z was --CH₂ N(CH₃)CH₂ CH₂ OH.

Water soluble resin 1 was synthesized as follows. 100 g of propyleneglycol monopropyl ether (a CELLOSOLVE™ solvent) was introduced into a1,000 mL reaction flask equipped with a condenser, nitrogen inlet tube,overhead stirrer, and thermometer, and 60 g of poly-4-vinylphenol(average molecular weight=5,000) was added and dissolved. 40 g of2-methylaminoethanol and 100 g of deionized water were added, and thiswas reacted by heating to 50° C. 40 g of 37% aqueous formaldehydesolution was added over 1 hour, followed by stirring at 50° C. for 2hours and by stirring for an additional 3 hours at 80° C. The reactionproduct was cooled, 15 g of 85% orthophosphoric acid was added, and 700g deionized water was also added. The resin was then precipitated by theaddition of 10% sodium hydroxide solution until the pH of the reactionsolution reached 8 to 9. The precipitated resin was filtered off, washedwith water, and dried.

Example 2

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 2 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. The treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface treatmentliquid composition 2 was also evaluated.

Surface-Treatment Liquid Composition 2

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

hypophosphorous acid (H₃ PO₂)

2.0 g/L (providing 1.9 g/L of PO₂ ³⁻ ions)

resin solids

0.4 g/L

pH=5.0 (adjusted with sodium carbonate)

The water soluble resin was the same as in Example 1.

Example 3

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface-treatment liquidcomposition 3 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface treatmentliquid composition 3 was also evaluated.

Surface-Treatment Liquid Composition 3

75% phosphoric acid (H₃ PO₄)

20.0 g/L (providing 14.4 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

phosphorous acid (H₃ PO₃)

1.0 g/L (providing 0.96 g/L of PO₃ ³⁻ ions)

hypophosphorous acid (H₃ PO₂)

1.0 g/L (providing 0.95 g/L of PO₂ ³⁻ ions)

resin solids

8.0 g/L

pH=4.0 (adjusted with sodium hydroxide)

The water soluble resin was the same as in Example 1.

Example 4

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 4 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 4 was also evaluated.

Surface-Treatment Liquid Composition 4

75% phosphoric acid (H₃ PO₄)

15.0 g/L (providing 10.9 g/: of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

2.5 g/L (providing 1.0 g/L of P₂ O₇ ⁴⁻ ions)

phosphorous acid (H₃ PO₃)

1.0 g/L (providing 0.95 g/L of PO₃ ³⁻ ions

resin solids

4.0 g/L

pH=3.0 (adjusted with sodium carbonate)

The water soluble resin was the same as in Example 1.

Example 5

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface-treatment liquidcomposition 5 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 5 was also evaluated.

Surface-Treatment Liquid Composition 5

75% phosphoric acid (H₃ PO₄)

30.0 g/L (providing 21.6 g/L of PO₄ ³⁻ ions)

sodium tripolyphosphate (Na₅ P₃ O₁₀)

0.6 g/L (providing 0.4 g/L of P₃ O₁₀ ⁵⁻ ions)

phosphorous acid (H₃ PO₃)

3.0 g/L (providing 2.9 g/L of PO₃ ³⁻ : ions)

resin solids

2.0 g/L

pH=3.5 (adjusted with sodium hydroxide)

The water soluble resin was the same as in Example 1.

Example 6

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 15-second spray of surface-treatment liquidcomposition 6 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 6 was also evaluated.

Surface-Treatment Liquid Composition 6

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g.L of P₂ O₇ ⁴⁻ ions)

hypophosphorous acid (H₃ PO₂)

2.0 g/L (providing 1.9 g/L of PO₂ ³⁻ ions)

resin solids

2.0 g/L of water soluble resin 2

pH=4.0 (adjusted with sodium hydroxide)

Water soluble resin 2 was the same as water soluble resin 1, except thatonly one-quarter rather than one-half of the X's and Y's in the generalformula were Z groups. Water soluble resin 2 was synthesized as forwater soluble resin 1 but with 60 g of poly-4-vinylphenol, 20 g of2-methylaminoethanol, and 20 g of 37% formaldehyde solution.

Example 7

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 7 heated to 50° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 7 was also evaluated.

Surface-Treatment Liquid Composition 7

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

phosphorous acid (H₃ PO₃)

2.0 g/L (providing 1.9 g/L of PO₃ ³⁻ ions)

resin solids

2.0 g/L of water soluble resin 3

pH=6.0 (adjusted with sodium hydroxide)

Water soluble resin 3 had an average value for n in the general formulaof 70, half of the X's and Y's in the general formula were Z, and Z was--CH₂ N(CH₃)₂. Water soluble resin 3 was synthesized as for watersoluble resin 1 but from 60 g of poly-4-vinylphenol, 23 g ofdimethylamine, and 40 g of 37% formaldehyde solution.

Example 8

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 8 heated to 40° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface treatmentliquid composition 8 was also evaluated.

Surface-Treatment Liquid Composition 8

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

hypophosphorous acid (H₃ PO₂)

2.0 g/L (providing 1.9 g/L of PO₂ ³⁻ ions)

resin solids

0.4 g/L of water soluble resin 4

pH=5.0 (adjusted with sodium carbonate)

Water soluble resin 4 was the same as water soluble resin 1, except thatthe average value of n in the general formula was only 3. Water solubleresin 4 was synthesized as for water soluble resin 1, but from 60 g ofpoly 4-vinylphenol with an average molecular weight of 360, 40 g of2-methylaminoethanol, and 40 g of 37% formaldehyde solution.

Comparison Example 1

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface-treatment liquidcomposition 9 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1 . Thistreated can was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 9 was also evaluated.

Surface-Treatment Liquid Composition 9

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

resin solids

0.4 g/L of water soluble resin 1 as in Example 1.

pH=5.0 (adjusted with sodium carbonate)

Comparison Example 2

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 10 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 10 was also evaluated.

Surface-Treatment Liquid Composition 10

75% phosphoric acid (H₃ PO₄)

20.0 g/L (providing 14.4 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

10 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

phosphorous acid (H₃ PO₃)

0.1 g/L (providing 0.095 g/L of PO₃ ³⁻ ions)

resin solids

8.0 g/L of water soluble resin 1 as in Example 1

pH=4.0 (adjusted with sodium hydroxide)

Comparison Example 3

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 11 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 11 was also evaluated.

Surface-Treatment Liquid Composition 11

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

resin solids

2.0 g/L of water soluble resin 1 as in Example 1

pH=4.0 (adjusted with sodium carbonate)

Comparison Example 4

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 12 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface treatmentliquid composition 12 was also evaluated.

Surface-treatment Liquid composition 12

75% phosphoric acid (H₃ PO₄)

1.0 g/L (providing 0.72 g/L of PO₄ ³⁻ ions)

resin solids

2.0 g/L of water soluble resin 1 as in Example 1

pH=7.0 (adjusted with sodium hydroxide)

Comparison Example 5

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 13 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface-treatmentliquid composition 13 was also evaluated.

Surface-Treatment Liquid Composition 13

75% phosphoric acid (H₃ PO₄)

10.0 g/L (providing 7.2 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g/L of P₂ O₇ ⁴⁻ ions)

resin solids

0.05 g/L of water soluble resin 1 as in Example 1

pH=4.0 (adjusted with sodium carbonate)

Comparison Example 6

Tin-plated DI can was cleaned using the same conditions as in Example 1and was then treated with a 30 second spray of surface treatment liquidcomposition 14 heated to 60° C. This treatment was followed with a waterrinse and drying using the same conditions as in Example 1. This treatedcan was subjected to an evaluation of the corrosion resistance,adherence, and slideability, and the stability of surface treatmentliquid composition 14 was also evaluated.

Surface-Treatment Liquid Composition 14

75% phosphoric acid (H₃ PO₄)

1.0 g/L (providing 0.72 g/L of PO₄ ³⁻ ions)

sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O)

1.0 g/L (providing 0.4 g.L of P₂ O₇ ⁴⁻ ions)

resin solids

2.0 g/L of water soluble resin 5

pH=4.0 (adjusted with sodium hydroxide)

Water-soluble resin 4 had the chemical formula: ##STR4## The averagevalue of n was about 40.

Water-soluble resin 4 was synthesized as follows: 50 g ofpoly{4-vinylphenol} (molecular weight=about 5,000) was placed in a 1,000mL reaction flask equipped with a condenser, nitrogen inlet tube,overhead stirrer, and thermometer, and 500 g of 1,4-dioxane was addedfor dissolution. An amount of 80 g of liquid sulfur trioxide (SO₃) wasadded over a time of 1 hour while the mixture was maintained at around10° C. This was followed by heating to 80° C. and reaction for 4 hourswhile stirring. Neutralization was carried out with 10% sodium hydroxidesolution and the solvent was distilled off.

The various results are reported in Table 1, and they confirm that thesurface treatment liquid compositions according to the present inventionhave excellent stability and also forms a film having an excellentcorrosion resistance, adherence, and slideability.

                  TABLE 1                                                         ______________________________________                                        TEST RESULTS                                                                               Peel Strength,                                                                            Friction                                                     IEV  kgf/5 mm-width                                                                            Coefficient                                                                              Stability                                 ______________________________________                                        Example 1 40     2.0         0.8      +                                       Example 2 40     2.0         0.8      +                                       Example 3 50     2.0         0.8      +                                       Example 4 40     2.0         0.8      +                                       Example 5 40     2.0         0.8      +                                       Example 6 60     2.0         0.8      +                                       Example 7 40     2.0         0.8      +                                       Example 8 60     2.0         0.8      +                                       Comparison                                                                              40     2.0         0.8      x                                       Example 1                                                                     Comparison                                                                              50     2.0         0.8      x                                       Example 2                                                                     Comparison                                                                              250    1.5         1.0      x                                       Example 3                                                                     Comparison                                                                              950    1.3         1.0      x                                       Example 4                                                                     Comparison                                                                              500    1.5         1.0      x                                       Example 5                                                                     Comparison                                                                              750    1.3         1.0      x                                       Example 6                                                                     ______________________________________                                         Notes for Table 1                                                             + = no precipitation                                                          x = precipitation                                                        

The invention claimed is:
 1. An aqueous liquid composition of matterhaving a pH in the range from 2.0 to 6.5 and comprising water and:(A)from 1 to 30 g/L of phosphate ions, (B) from 0.1 to 5 g/L of condensedphosphate ions, (C) from 0.5 to 5 g/L of reducing agent, and (D) from0.1 to 20 g/L of dissolved solids of a water soluble resin componentselected from molecules conforming to the following general formula:##STR5## where, in the preceding formula, n is an integer with a valuein the range from 2 to 80; each of X and Y independently of each otherand independently for each of the n units in the molecule may representhydrogen or a group "Z" with the following general formula: ##STR6## inwhich each of R₁ and R₂ independently of each other and independentlyfor each Z group in the component represents a C₁ to C₁₀ alkyl orhydroxyalkyl moiety, except that the total number of Z groups present inthe resin component is from 30 to 200% of the total number of aromaticrings in the resin component.
 2. A liquid composition according to claim1, wherein the groups Z in the general formula have one of the followingformulas: ##STR7##
 3. A liquid composition according to claim 2, whereinthe condensed phosphate ions are selected from the group consisting ofpyrophosphate ions, tripolyphosphate ions, tetrapolyphosphate ions, andmixtures thereof.
 4. A liquid composition according to claim 1, whereinthe condensed phosphate ions are selected from the group consisting ofpyrophosphate ions, tripolyphosphate ions, tetrapolyphosphate ions, andmixtures thereof.
 5. A liquid composition according to claim 4, whereinthe reducing agent component is selected from the group consisting ofphosphorous acid, hypophosphorous acid, salts of phosphorous andhypophosphorous acids, and mixtures of any two or more of phosphorousand hypophosphorous acids and salts of phosphorous and hypophosphorousacids.
 6. A liquid composition according to claim 3, wherein thereducing agent component is selected from the group consisting ofphosphorous acid, hypophosphorous acid, salts of phosphorous andhypophosphorous acids and mixtures of any two or more of phosphorous andhypophosphorous acids and salts of phosphorous and hypophosphorousacids.
 7. A liquid composition according to claim 2, wherein thereducing agent component is selected from the group consisting ofphosphorous acid, hypophosphorous acid, salts of phosphorous andhypophosphorous acids and mixtures of any two or more of phosphorous andhypophosphorous acids and salts of phosphorous and hypophosphorousacids.
 8. A liquid composition according to claim 1, wherein thereducing agent component is selected from the group consisting ofphosphorous acid, hypophosphorous acid, salts of phosphorous andhypophosphorous acids and mixtures of any two or more of phosphorous andhypophosphorous acids and salts of phosphorous and hypophosphorousacids.
 9. A liquid composition according to claim 8, wherein the amountof component (A) is in the range from 5 to 15 g/L, the amount ofcomponent (B) is in the range from 0.4 to 1 g/L, and the amount ofcomponent (C) is in the range from 1 to 3 g/L.
 10. A liquid compositionaccording to claim 7, wherein the amount of component (A) is in therange from 5 to 15 g/L, the amount of component (B) is in the range from0.4 to 1 g/L, and the amount of component (C) is in the range from 1 to3 g/L.
 11. A liquid composition according to claim 6, wherein the amountof component (A) is in the range from 5 to 15 g/L, the amount ofcomponent (B) is in the range from 0.4 to 1 g/L, and the amount ofcomponent (C) is in the range from 1 to 3 g/L.
 12. A liquid compositionaccording to claim 5, wherein the amount of component (A) is in therange from 5 to 15 g/L, the amount of component (B) is in the range from0.4 to 1 g/L, and the amount of component (C) is in the range from 1 to3 g/L.
 13. A liquid composition according to claim 4, wherein the amountof component (A) is in the range from 5 to 15 g/L, the amount ofcomponent (B) is in the range from 0.4 to 1 g/L, and the amount ofcomponent (C) is in the range from 1 to 3 g/L.
 14. A liquid compositionaccording to claim 3, wherein the amount of component (A) is in therange from 5 to 15 g/L, the amount of component (B) is in the range from0.4 to 1 g/L, and the amount of component (C) is in the range from 1 to3 g/L.
 15. A liquid composition according to claim 2, wherein the amountof component (A) is in the range from 5 to 15 g/L, the amount ofcomponent (B) is in the range from 0.4 to 1 g/L, and the amount ofcomponent (C) is in the range from 1 to 3 g/L.
 16. A liquid compositionaccording to claim 1, wherein the amount of component (A) is in therange from 5 to 15 g/L, the amount of component (B) is in the range from0.4 to 1 g/L, and the amount of component (C) is in the range from 1 to3 g/L.
 17. A process for treating a tin plated steel surface bycontacting the surface for a time from 2 to 60 seconds with acomposition according to claim 1 at a temperature in the range from 20°to 80° C.
 18. A process according to claim 17, where the temperature isin the range from 40° to 60° C.
 19. A process for treating a tin platedsteel surface by contacting the surface for a time from 2 to 60 secondswith a composition according to claim 12 at a temperature in the rangefrom 40° to 60° C.
 20. A process for treating a tin plated steel surfaceby contacting the surface for a time from 2 to 60 seconds with acomposition according to claim 2 at a temperature in the range from 20°to 80° C.